//  Copyright 2020  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.

package importer

import (
	"fmt"

	"google.golang.org/api/compute/v1"
)

// validator is the interface for performing validations.
//
// validate returns nil when passing, and non-nil when failing.
type validator interface {
	validate() error
}

func newPreValidator(request ImageImportRequest, client getImageClient) validator {
	return validateImageNameAvailable{
		project: request.Project,
		name:    request.ImageName,
		client:  client,
	}
}

// validateImageNameAvailable is an importer.validator that
// ensures the user's destination image name hasn't already
// been used.
type validateImageNameAvailable struct {
	project, name string
	client        getImageClient
}

func (v validateImageNameAvailable) validate() error {
	// We ignore the error, with the assumption that if there's an error,
	// then the image name may be available.
	image, _ := v.client.GetImage(v.project, v.name)
	if image != nil {
		return fmt.Errorf("The resource '%s' already exists. "+
			"Please pick an image name that isn't already used.", v.name)
	}
	return nil
}

// diskClient is the subset of the GCP API that is used by validateImageNameAvailable.
type getImageClient interface {
	GetImage(project, name string) (*compute.Image, error)
}
